Reducing Time Dependent Line to Line Leakage Following Post CMP Clean
- PDF / 330,156 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 165 Views
1249-E01-09
Reducing Time Dependent Line to Line Leakage Following Post CMP Clean Donald F. Canaperi1, Satyavolu S. Papa Rao2, Trace Q. Hurd3, Steven B. Medd3, T. M. Levin1, Christopher J. Penny1, James H.-C. Chen1, Matthew A. Smalley1 1 IBM at Albany Nanotech, Albany, NY,12203, USA, 2IBM Research, Yorktown Heights, NY, 10598, USA, 3ATMI Inc, Danbury, CT, 06810, USA. ABSTRACT A systematic approach was taken to identify methods to prevent post CMP corrosion of copper in 22nm interconnect structures. Line to line current leakage measurements (at various times post CMP) were used as a means to quantify the extent and time-dependence of copper corrosion. Interruption of the corrosion mechanism by the use of passivating agents in post-CMP clean chemistries is explored. A broad-based screening was conducted to identify aqueous formulations of passivating agents for protection of copper which do not have deleterious effects on line resistance and overall defectivity. A formulation was identified which was effective in preventing corrosion when applied during post CMP brush clean. INTRODUCTION Post-CMP corrosion of copper interconnects has been observed in earlier technology nodes. But at the 22nm node, it has become a critical problem impacting yield and reliability. Corrosion involves the formation of Cu ions at the surface due to oxidation under an electrochemical driving force and the motion of these ions. Moisture is also present in a postCMP wafer, particularly with ultra low-k dielectrics, forming an electrolytic medium. In the presence of moisture at the surface of a dense dielectric, photo-induced corrosion of copper has been reported in the literature [1]. For photo-induced corrosion, Cu corrosion is facilitated by light-induced bias due to p-n junctions that are connected to different Cu lines. However, since stress, impurities can result in locally cathodic and anodic regions in the Cu lines [2], corrosion can occur even between metal lines that are not connected to the silicon substrate. The influence of the galvanic couple formed by Cu and Ru-based liner materials in enhancing the probability of corrosion of Cu has also been reported [3]. If the copper surface is passivated however, such corrosion can be avoided. Deposition of a dielectric capping layer typically protects the interconnect structure, but at the current rates of corrosion, the allowable queue time to capping is becoming impractical. In the present study, interruption of the corrosion mechanism is explored through protection of the exposed copper surface through application of a passivating film in the post-CMP cleaning process. The relative rate of corrosion for each treatment is quantified though repeated line-to-line leakage measurements on 22nm-node test patterns.
EXPERIMENT A broad-based screening study was conducted to identify passivating compounds with supporting aqueous matrices which can be effective towards the unique challenge of preventing corrosion of copper for interconnects at the 22nm node. Interconnect test patterns were fabr
Data Loading...
